Add invoice SMS notifications and customer intake kiosk

Invoice SMS:
- Send Invoice modal now prompts Email/SMS/Both based on customer contact data
- New /invoice/{token} customer-facing view page with full line items and pay button
- PublicViewToken (permanent) added to Invoice; separate from expiring PaymentLinkToken
- InvoiceSent SMS default template added; customizable via Notification Templates settings
- {{viewUrl}} placeholder documented in template editor

Customer Intake Kiosk:
- Tablet kiosk flow: Contact → Job → Terms/Signature → Confirmation
- Remote link mode for off-site customers (lighter form, no signature)
- KioskHub (AllowAnonymous SignalR) for staff-to-tablet push without login
- Staff activates tablet via cookie; sends remote link manually
- Submitted sessions create Customer + Job automatically; fires in-app notification

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Core/Interfaces/IUnitOfWork.cs

@@ -154,6 +154,9 @@ public interface IUnitOfWork : IDisposable
     IRepository<GiftCertificate> GiftCertificates { get; }
     IRepository<GiftCertificateRedemption> GiftCertificateRedemptions { get; }
 
+    // Customer Intake Kiosk
+    IRepository<KioskSession> KioskSessions { get; }
+
     Task<int> SaveChangesAsync();
     Task<int> CompleteAsync(); // Alias for SaveChangesAsync